# -*- coding: utf-8 -*-
"""
Created on Fri May  3 16:42:03 2024

@author: Administrator
"""

a=int(input("请输入"))
if 70>a>=60:
    print('D')
elif 80>a>=70:
    print('C') 
elif 90>a>=80:
    print('B')
elif a>=90:
    print('A')
else:
    print('e')
    